The invention relates to a method and a device for sliding and positioning sleeve-shaped, elastic, radially expandable components on cylindrical or conical base bodies having a smallest outer diameter to be covered or enclosed which is greater than the non-expanded inner diameter of the sleeve-shaped component to be mounted. Preferably, the invention has as objective to slide such radially expandable, sleeve-shaped components on base bodies made from insulated cable wires or cable wire bundles prepared in a manner known per se.
An important field of application of the method according to the invention and of the device for implementing the method thus includes to slide and position components of cable fittings on base bodies in the form of cable ends or cable connections which have been prepared in a manner known per se for making insulated cable connections for single-conductor and three-conductor plastic cables carrying nominal voltages of about 30 kV.
Upon application of the method in the cable connection technique and cable insulation technique, the preferably employed, conventional expandable sleeve-shaped components are made for example from silicone rubber or EPDM and can be modified, depending on the application, with fillers in order to effect e.g. a field control or to increase the leakage current resistance. In particular, these components can also be constructed of several elastic layers, e.g. layers having a different conductivity and/or dielectric constant, and are used for assembling cable fittings, i.e. for providing an insulation at the ends of a cable in conjunction with cable terminations, cable plugs, as cable end caps, or as cable sleeves for insulation at the point of connection between two cable ends, and thus form part of a cable fitting set.
In these cases, the base body to be enclosed is an insulated cable wire or an insulated cable wire bundle, preferably from plastic cables with polyethylene insulation, with the outer sheath, including the so-called outer conductor layer, being removed, as is customary when the cable fittings are installed. If necessary, prior to sliding and positioning of the elastically expandable sleeve-shaped component, the insulating layer of the cable is provided with an enveloping layer which forms e.g. a barrier against escape of cable mass in paper insulated mass-impregnated cables.
Conventionally, when the sleeve-shaped components are fitted over and positioned on the cable ends prepared in a conventional manner, e.g. over a completed cable connection, the component is usually pulled by hand over the cable connection or cable end region, requiring a great exertion of force. In order to ensure that the cable connection, including the cable ends on both sides and the regions where the cable exits the cable sleeve, is sealed reliably, the inner diameter of the sleeve-shaped component in its relaxed state must be sufficiently smaller than the smallest outer diameter of the cable connection or cable end to be enclosed.
A potential problem, however, exists in that the prepared cable wire connections and the conductor cross sections can be very different in thickness and outer diameter, respectively. In order to ensure a tight enclosure with sufficient tension even at the thinnest regions at the ends of the cable wire connection and the conductor cross section, the sleeve-shaped component must be so dimensioned as to provide a sufficient enveloping force in the relaxed state also in these thin regions. Since the sleeve-shaped components are available with graduated dimensional sizes, it may happen that such a component is not wide enough even in the stretched state in order to allow easy sliding over the prepared cable connection; In these situations, which are typically carried out manually, the assembler is required to apply a significant force which increases with increasingly required expansion of the sleeve-shaped component.
The required force is also dependent on the material of which the components that move relative to one another are made from. When cable connections are made using conventional technology, the sleeve-shaped component made from silicone rubber or EPDM is fitted over the cable insulation made of polyethylene; This has frequently proven to be difficult since silicone tends to "adhere" to polyethylene.
It is known to enable or ease the sliding of the sleeve-shaped component by use of a lubricant, e.g. a lubricating gel or a slip sheet. There are, however, limitations to the effectiveness of known lubricants.
It is known from German Pat. Nos. DE 37 15 915 A1 and DE 30 01 158 A1 to place the sleeve-shaped component, before assembly, on a relatively rigid or slightly plastically deformable cylindrical support device which is then pushed together with the sleeve-shaped component on the cable prepared for assembly, at formation of a radial spacing therebetween. The support device, such as a helical support or a single-part or multi-part support sleeve, is removed after the component is in place. This procedure is however disadvantageous in view of the considerable demand of material and high costs for the support device and the considerable, and in the one case also extended expansion of the sleeve-shaped components of the cable fitting over the entire storage period. Expansion of sometimes more than 300% can lead during this long storage period to the formation of cracks or to material fatigue, thereby preventing reliable insulation and sealing. Since storage periods are typically up to 3 years, the unavoidable material fatigue reduces after relaxation the remaining contact pressure upon the cable and wire insulation. As a result, insufficient insulation can be experienced, leading to partial discharge between the cable and wire insulation and the inner surface of the sleeve-shaped insulating component of the cable fitting; This, however, has to be prevented for reasons of operational safety.
International patent specification WO 89/00782 A1 discloses a method which suggests to use slide rails in parallel and lateral contacting disposition for insertion into a sleeve, with the slide rails having narrow sides provided with longitudinally extending profiles which engage in form-fitting manner with one another, thereby forming a closed annular jacket-like cylindrical structure to effect reduced friction and facilitate a mounting thereof. A drawback however is that the diameter of the jacket-like structure is determined by the number and dimensions of the slide rails so that differences in the diameter e.g. smaller diameters can only be accommodated by the jacket-like structure through an undesirable overlap of these rails.